A large number of abdominal surgical procedures are performed with laparoscopic techniques in order to avoid a large skin incision. Typically in laparoscopic surgery, a special needle (e.g. a needle similar to the needles described in U.S. Pat. No. 4,808,168 and U.S. patent application Ser. No. 07/808,152, both of which are herein expressly incorporated by reference) is inserted through the skin, and used to inflate the abdominal cavity with an insufflating gas such as carbon dioxide (CO.sub.2). Once the abdomen is adequately dilated, the needle is removed and a rigid access tube or cannula with a diameter larger than the pneumoneedle (for example 5, 10 or 11 mm) is passed through the skin in generally the same location.
The access tube provides access for laparoscopic surgical tools such as a laparoscope, the stapler described in U.S. Pat. No. 5,040,715 or the surgical clip appliers described in U.S. Pat. Nos. 5,084,057 and 5,100,420. To drive the access tube through the skin, the surgeon places a trocar in the lumen of the access tube to provide a sharp leading edge for cutting tissue.
The art is replete with trocar devices, including those shown in U.S. Pat. Nos. 4,535,773, 4,601,710, 4,654,030, 4,902,280 and 4,931,042. Those trocars typically comprise an obturator with cutting surfaces for penetrating the skin, and a spring-loaded protective sleeve that surrounds the obturator. As these trocar devices are urged through the skin, friction with the skin causes the protective sleeve to slide proximally (rearwardly). After the access tube has penetrated through the skin, there is no longer friction between the protective sleeve and the skin, and the spring is designed to urge the protective sleeve distally (forwardly) to cover the cutting surfaces. Some of those trocars lock the protective sleeve in the forward position to reduce the risk of accidental puncture of the underlying organs.
These prior art trocars rely on a similar principle of operation: the friction or drag on the protective sleeve as the trocar is advanced through the skin pushes the protective sleeve back (proximally) to expose the cutting surfaces. Once the access tube has penetrated the skin, the drag on the protective sleeve is reduced and the sleeve accelerates distally (forwardly) under the bias of the spring to cover the cutting surfaces.
Those existing trocars encounter problems because a significant amount of force usually must be applied to penetrate the skin (particularly the tough fascia). As a result of the significant insertion force, the trocar may continue to advance toward the underlying organs after it has penetrated the skin. The protective sleeve must "catch up" to the moving trocar point before the trocar reaches the underlying organs. This action may be delayed if the protective sleeve is hung up on tissue.
In addition to the prior art trocars described above, several documents disclose trocars which ultimately retract the obturator relative to the cannula after the obturator has pierced the tissue of abdominal wall. Such documents include U.S. Pat. Nos. 4,535,773 to Yoon, 5,116,353 to Green (and related European Patent Publication 0 479 130), U.S. Pat. Nos. 5,104,382 to Brinkerhoff et al. and 5,152,754 to Plyley et al. Additionally, a trocar having an obturator which ultimately retracts relative to the cannula has been on sale in this country by Origin Medsystems, Inc. prior to the filing date of the present application.
However, with the trocar sold by Origin Medsystems, Inc. and the trocars described in U.S. Pat. No. 5,116,353 to Green (and related European Patent Publication 0 479 130), the obturator first moves distally away from the cannula (and thus toward the underlying organs) in order to actuate the mechanism which ultimately retracts the obturator relative to the cannula. This distal movement occurs just at the time when it is least desirable, that is, the distal movement of the obturator relative to the cannula occurs when the obturator pierces the tissue of the abdominal wall, clearly an undesirable result.
U.S. Pat. No. 5,152,754 discloses a trocar comprising an obturator which retracts relative to the access tube just after the obturator pierces the tissue defining the body cavity. U.S. Pat. No. 5,104,382 also discloses an obturator which retracts relative to a cannula. However, in each of U.S. Pat. Nos. 5,152,754 and 5,104,382, the devices include a member between the obturator and the cannula which necessarily limits the size of the obturator. For example, Brinkerhoff et al., U.S. Pat. No. 5,104,382, includes a shield between the obturator and cannula.